US3895367A - Gas indicator with semiconductive gas sensor - Google Patents

Gas indicator with semiconductive gas sensor Download PDF

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Publication number
US3895367A
US3895367A US437351A US43735174A US3895367A US 3895367 A US3895367 A US 3895367A US 437351 A US437351 A US 437351A US 43735174 A US43735174 A US 43735174A US 3895367 A US3895367 A US 3895367A
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Prior art keywords
gas
gate
voltage
circuit
oscillator
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US437351A
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Robertus Gerardus Visser
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    • G—PHYSICS
    • G08—SIGNALLING
    • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B17/00—Fire alarms; Alarms responsive to explosion
    • G08B17/10—Actuation by presence of smoke or gases, e.g. automatic alarm devices for analysing flowing fluid materials by the use of optical means
    • G08B17/117—Actuation by presence of smoke or gases, e.g. automatic alarm devices for analysing flowing fluid materials by the use of optical means by using a detection device for specific gases, e.g. combustion products, produced by the fire
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
    • G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
    • G01N27/12—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a solid body in dependence upon absorption of a fluid; of a solid body in dependence upon reaction with a fluid, for detecting components in the fluid
    • G01N27/122—Circuits particularly adapted therefor, e.g. linearising circuits

Definitions

  • the gas indicator is operated by means of two bistable circuits, changing their states, respectively, at [52] US. Cl 340/237 R; 340/237 S the end of the activating time of the body, and upon [51] Int. Cl. G08b 17/10 occurrence of a gas.
  • the output signals of the two bis- [58] Field of Search 340/237 R; 23/254 E table circuits actuate an alarm circuit by means of a coincidence circuit.
  • the filament of the gas sensor [56] References Cited may be fed by the output energy of an oscillator.
  • the invention relates to a gas indicator provided with a gas sensor consisting of a body of a semiconductive material incorporating two spaced electrodes of which one is constructed as a filament for heating the body, which is activated by the heating and thereby obtains the property that the electric resistivity is considerably reduced when the body is exposed to a gas, the current path between the electrodes of the sensor being inserted in a circuit containing a current source, so that the decrease of the resistivity gives rise to a current change whereby an alarm circuit is actuated.
  • a known sensor of the above-mentioned kind consists of an N-type metal oxide, such as tin oxide, zinc oxide, or ferric sesquioxide, and is sensitive, inter alia, to hydrogen, carbon monoxide, methane, propane, volatile oils, acetylene. smoke, and carbon containing air.
  • N-type metal oxide such as tin oxide, zinc oxide, or ferric sesquioxide
  • the resistance occurring between the electrodes is small when the semiconductive body is at room temperature.
  • the resistance between the electrodes obtains gradually a very high value.
  • a final condition is reached in which the sensor has a maximum activity.
  • the semiconductive body is now exposed to a gas, such as carbon monoxide, hydrogen, hydrocarbons, or the like, the resistance between the electrodes is considerably reduced, whereby the alarm circuit may be actuated.
  • the heating time about one minute. the operation of the alarm circuit must be inhibited.
  • Another object of the invention is to provide a gas indicator of the above-mentioned kind adapted to be constructed as a portable apparatus.
  • a gas indicator is constructed in such manner that the operation of the alarm circuit is inhibited during the activating time by a delay circuit controlling a first bistable circuit changing its state at the end of the activating time, and the current flowing through the semiconductive body in the presence of a gas to which the sensor is sensitive causes a change of state of a second bistable circuit, the output signals of the two bistable circuits occurring after their changes of state being supplied to a coincidence circuit actuating the alarm circuit when both output signals are present.
  • the gas indicator according to the invention is desirable to construct as a portable apparatus, which may be carried along by persons working, for instance, in a mine, 5 ship hold or a sewer, so that they are warned upon the occurrence of harmful gases.
  • a portable apparatus of this kind may also be arranged in a motor car to warn the passengers upon the occur rence of carbon monoxide.
  • Such a portable apparatus would. of course. have to be fed by a battery, which ought to have a voltage of at least 6 volts, and preferably of l2 volts in order to obtain a sufficient energy for the alarm circuit.
  • a battery which ought to have a voltage of at least 6 volts, and preferably of l2 volts in order to obtain a sufficient energy for the alarm circuit.
  • this leads to some difficulties in connection with the feeding of the filament which is laid out for a voltage of one volt at a current of one ampere.
  • the required current of one ampere can only be furnished during a short time by a battery having a reasonable weight, and a series resistor must be used to reduce the battery voltage to the voltage of one volt required for the filament, whereby a considerable energy is lost.
  • This difficulty may be removed by using, as a current source, a D.C. source also feeding an oscillator of which the output energy feeds the filament.
  • a D.C. source also feeding an oscillator of which the output energy feeds the filament.
  • the use of an oscillator for feeding the filament leads to an important additional advantage. If the oscillator frequency is suitably chosen, it is possible to insert a piezo-electric sound generator fed by the oscillator in the alarm circuit. so that a very strong acoustic alarm is obtained by simple means.
  • the oscillator voltage may be supplied to a third input terminal of the coincidence circuit.
  • a voltage is supplied. when the indicator is switched on. to the series circuit of a resistor and a condenser.
  • the first bistable circuit being constructed as a Schmitt trigger controlled by the voltage across the condenser, so that the first bistable circuit delivers a l-signal during the activating time and a O-signal after termination of the activating time, said 0-signal being inverted and the lsignal obtained by this inversion being simultaneously supplied to one of the input terminals of a nand-gate, and through a series resistor to the base of an emitter follower; furthermore, the current path between the electrodes of the sensor is connected between the base of said emitter follower and ground, and the emitter voltage of said emitter follower is supplied to the second bistable circuit.
  • the above-mentioned inversion of the O-signal of the first bistable circuit may be performed by a third bistable circuit constructed as an inverting Schmitt trigger.
  • FIG. 1 shows a gas indicator according to the invention which is fed by a D.C. current source. so that it may be constructed as a portable apparatus;
  • FIG. 2 shows a gas indicator according to the invention which may be fed from A.C. mains.
  • the circuit arrangement shown in FIG. 1 is fed by a DC. source having a voltage of 12 volts. and connected with the terminals 1 and 2.
  • the gas sensor proper consists of a semiconductive body 3, incorporating two electrodes 4 and 5.
  • the electrode 4 hasa helical shape and serves as a filament for activating the sensor.
  • the electrode 5 may, in principle, have any desired shape; however, it is generally also shaped as a helix, so. that each of the electrodes4 and 5 may be used as a filament, as desired.
  • An oscillator 6 operating, for instance, at a frequency of the order of 800 cycles per second, is connected with the terminals 1 and 2.
  • the output energy of the oscillator is supplied to the filament 4 through a transformer 7. V
  • the filament 4 is also connected with the positive terminal 1 of the DC. source, so that the entire voltage of this source is available for controlling the alarm circuit.
  • the alarm circuit is blocked.
  • Use is made, for this purpose, of a delay circuit provided with a condenser 8, which is charged by the source through an adjustable resistor 9. After 1 minute, the voltage across condenser 8 has obtained such a value that a unijunction transistor 10 is rendered conductive. A voltage impulse is thereby generated across a resistor 11, and supplied through a resistor 12 to the l-input terminal of a bistable circuit 13.
  • the voltage occurring at the l-output terminal of the circuit 13 is supplied to one of the input terminals of an andgate 14
  • the ()-input terminal of the circuit 13 is connected with the terminal 1 through the series connection of a resistor 15 and a condenser 16, so that the circuit 13 is always brought into its O-condition when the indicator is connected with the DC. source.
  • the electrode 5 of the sensor is connected with a resistor 17, and with the input terminal of a Schmitt trigger 18.
  • a current flows through resistor 17, whereby the trigger 18 changes its state.
  • the output terminal of the trigger 18 is connected with a second input terminal of the andgate 14.
  • the oscillator voltage is supplied through a conduc' tor 19 to the third input terminal of the and-gate 14.
  • the output circuit of the and-gate 14 contains a piezoelectric sound generator 20 tuned to the oscillator frequency.
  • the transformer 7 may form a part of the frequency determining circuit of the oscillator 6, and may be provided with a third winding for feed-back purposes.
  • the inhibition of the alarm circuit during the activating time is also obtained by means of a delay circuit comprising acondenser 8 and a resistor 9; this delay circuit is connected with a DC. voltage whenthe indicator is switched on.
  • the voltage across condenser 8 controls a Schmitt trigger consisting of two transistors 21 and 22 having a common emitter resistor; the collector of each transis-
  • the O-signal in line 23 is converted into a l-signal by means of an inverting Schmitt trigger 24, this l-signal is supplied to one of the input terminals of a nand-gate 25, and through an adjustable series resistor 26 to the base ofan emitter follower 27.
  • the base of transistor 27 is also connected with the electrode 5 of the sensor 3;.the filament 4is fed with an A.C. voltage of l volt at a current of one ampere, derived from the A.C. mains by means of .a transformer.
  • the activated sensor has ahigh resistance, so that the base voltage of transistor 27 is not influenced by the sensor. ln this case, the emitter of transistor 27 carries a 1-signal, which is supplied to an inverting Schmitt trigger 28, so that this trig,-.
  • This O-signal is supplied to the second input terminal of the nand-gate 25, and through two inverting amplifiers 29 and 30 to a green indicating lamp 31, so that this lamp is ignited to indicate that no gas,.is present.
  • the base of transistor 27 Upon occurrence of agas to which the sensor is sensitive, the base of transistor 27 is grounded through a small resistance. so thatthe emitter delivers a ()-signal which is converted into a l-signal by the trigger 28.
  • the green lamp 3] is now extinguished, and both input terminals of the nand-gate 25 carry l-signals, so that the gate is operated and delivers a 'O-signal, which is converted into a l-signal by an inverting amplifier 32.
  • This l-signal is supplied to one of the ends of a relay coil 33, of which the other end is connected with the l-voltage. so that the relay is de-energized.
  • a back contact of the relay actuates means for removing the dangerous condition, such as an exhauster.
  • an inverting amplifier 34 a red indicating lamp 35 is ignited, indicating a dangerous condition.
  • the l-signal at the output terminal of amplifier 32 is also supplied to one of the input terminals of a nandgate 36, of which the other input terminal is connected with an oscillator 37.
  • the oscillator signal is now supplied through amplifiers 38 and 39 to a loudspeaker 40, whereby an acoustic alarm is obtained.
  • the above-described circuit arrangement may be composed of integrated circuits, in such manner that the triggers 24 and 28 are incorporated in a first integrated circuit, the amplifiers 29, 30, 32, 34, 38 and 39 in a second integrated circuit, and the gates 25 and 26, together with the oscillator 37, in a third integrated circ'uit. It will be understood that the assembly of the circuit arrangement is rendered very simple in this manner.,
  • the DC. voltage for feeding the various parts of the circuit arrangement may, for instance, amount'to 5 volts, and is derived from the A.C. mainsvoltage by transformation and rectification.
  • thermal devices may be used for the inh ibition of the alarm circuit during the activating time, for instance a bimetalswitch or a resistarice with a negative temperature coefficient.
  • the thermal device is gradually heated after the gas indicator has been switched on, so that it may bring about a changeover after expiration of the desired activating time.
  • a gas indicator comprising a semiconductive body serving as a gas sensor adapted to be thermally activated and having in activated condition the property that the resistivity thereof is substantially reduced upon exposure to a gas, a first electrode incorporated in said body and shaped as a filament for activating the same, an alternating current source, means for connecting said alternating current source across said first electrode, a second electrode incorporated in said body and spaced with respect to said first electrode, a circuit interconnecting the said electrodes and including a direct current source, a current change occurring in the said circuit when the resistivity of said body is reduced, a delay circuit coupled to said direct current source and actuated when the indicator is energized, a first trigger controlled by said delay circuit to change state at the end of a determinable activating time, a second trigger controlled by said current change so as to change state when the resistivity of said body is re depictd, a coincidence gate controlled by output signals of the said triggers occurring after their changes of state. and an alarm circuit actuated by the output signal of said coincidence gate
  • a gas indicator as claimed in claim 1 further comprising means for supplying the output voltage of said oscillator as a heating voltage to the ends of said first electrode.
  • a gas indicator as claimed in claim 2 further comprising a piezo-electric sound generator inserted in said alarm circuit, and means for supplying the output voltage of said oscillator as an energizing voltage to said sound generator.
  • a gas indicator comprising a semiconductive body serving as a gas sensor, adapted to be thermally activated and having, in activated condition, the property that the resistivity thereof is substantially reduced upon exposure to a gas, a first electrode incorporated in said body and shaped as a filament for activating the same. an alternating current source coupled across said first electrode.
  • a second electrode incorporated in said body and spaced with respect to said first electrode, a circuit interconnecting the said electrodes, a direct current source coupled to said interconnecting circuit such that a current change occurs in the same when the resistivity of said body is reduced, a delay circuit including a first resistor and a condenser in series with said first resistor, a first Schmitt trigger controlled by the voltage across said condenser so as to deliver a l-signal during the activating time of said body and a O-signal after expiration of said activating time, a second inverting Schmitt trigger, an inverter controlled by the O-signal of said first trigger, a nand-gate having at least two input terminals, means for supplying the output signal of said inverter to one of the said input terminals, a second resistor, an emitter follower having a base, an emitter and a collector, means for supplying the output signal of said inverter throught said second resistor to the base of said emitter follower,

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  • Chemical & Material Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Analytical Chemistry (AREA)
  • General Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Emergency Management (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Business, Economics & Management (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Emergency Alarm Devices (AREA)
  • Fire-Detection Mechanisms (AREA)
  • Investigating Or Analyzing Materials By The Use Of Fluid Adsorption Or Reactions (AREA)
US437351A 1973-10-10 1974-01-28 Gas indicator with semiconductive gas sensor Expired - Lifetime US3895367A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
NL7313897A NL7313897A (nl) 1973-10-10 1973-10-10 Gasindicator.

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US3895367A true US3895367A (en) 1975-07-15

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US (1) US3895367A (enrdf_load_stackoverflow)
JP (1) JPS5067197A (enrdf_load_stackoverflow)
BE (1) BE808064A (enrdf_load_stackoverflow)
DE (1) DE2402493A1 (enrdf_load_stackoverflow)
FR (1) FR2247773B1 (enrdf_load_stackoverflow)
NL (1) NL7313897A (enrdf_load_stackoverflow)

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4007456A (en) * 1975-12-01 1977-02-08 Craftor Inc. Gas detecting and warning system
US4065759A (en) * 1976-01-07 1977-12-27 Handing Theodore E Smoke detector
US4088986A (en) * 1976-10-01 1978-05-09 Boucher Charles E Smoke, fire and gas alarm with remote sensing, back-up emergency power, and system self monitoring
US4096473A (en) * 1976-12-09 1978-06-20 P.R. Mallory & Co. Inc. High output smoke and heat detector alarm system utilizing a piezoelectric transducer and a voltage doubling means
US4185491A (en) * 1977-01-10 1980-01-29 British Steel Corporation Gas monitors
US4225860A (en) * 1979-01-15 1980-09-30 Pittway Corporation Sensitivity controlled dual input fire detector
USRE30620E (en) * 1978-07-03 1981-05-19 P. R. Mallory & Co. Inc. High output smoke and heat detector alarm system utilizing a piezoelectric transducer and a voltage doubling means
US4306229A (en) * 1976-03-17 1981-12-15 Nohmi Bosai Kogyo Co., Ltd. Smoke detector having an integral piezo-electric buzzer
US4335379A (en) * 1979-09-13 1982-06-15 Martin John R Method and system for providing an audible alarm responsive to sensed conditions
US4345612A (en) * 1979-06-12 1982-08-24 Citizen Watch Company Limited Anesthetic gas control apparatus
CN110164066A (zh) * 2017-12-29 2019-08-23 郑州天舜电子技术有限公司 一种安全警戒指示灯

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CH598601A5 (enrdf_load_stackoverflow) * 1975-07-10 1978-05-12 Richard Hunziker
FR2431124A1 (fr) * 1978-07-11 1980-02-08 Silvy Bruno Appareil de detection d'alcoolemie
IT212760Z2 (it) * 1985-02-13 1989-09-20 Salutati Giovanni Pistolozzi M Sistema di protezione contro le fughe di gas 'protector-gas'
DE102014019773B4 (de) 2014-12-17 2023-12-07 Elmos Semiconductor Se Vorrichtung und Verfahren zur Unterscheidung von festen Objekten, Kochdunst und Rauch mittels des Displays eines Mobiltelefons
DE102014019172B4 (de) 2014-12-17 2023-12-07 Elmos Semiconductor Se Vorrichtung und Verfahren zur Unterscheidung von festen Objekten, Kochdunst und Rauch mit einem kompensierenden optischen Messsystem

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3733595A (en) * 1971-02-12 1973-05-15 E Benedict Condition responsive switching circuit

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5320668Y2 (enrdf_load_stackoverflow) * 1972-06-07 1978-05-31

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3733595A (en) * 1971-02-12 1973-05-15 E Benedict Condition responsive switching circuit

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4007456A (en) * 1975-12-01 1977-02-08 Craftor Inc. Gas detecting and warning system
US4065759A (en) * 1976-01-07 1977-12-27 Handing Theodore E Smoke detector
US4306229A (en) * 1976-03-17 1981-12-15 Nohmi Bosai Kogyo Co., Ltd. Smoke detector having an integral piezo-electric buzzer
US4088986A (en) * 1976-10-01 1978-05-09 Boucher Charles E Smoke, fire and gas alarm with remote sensing, back-up emergency power, and system self monitoring
US4096473A (en) * 1976-12-09 1978-06-20 P.R. Mallory & Co. Inc. High output smoke and heat detector alarm system utilizing a piezoelectric transducer and a voltage doubling means
US4185491A (en) * 1977-01-10 1980-01-29 British Steel Corporation Gas monitors
USRE30620E (en) * 1978-07-03 1981-05-19 P. R. Mallory & Co. Inc. High output smoke and heat detector alarm system utilizing a piezoelectric transducer and a voltage doubling means
US4225860A (en) * 1979-01-15 1980-09-30 Pittway Corporation Sensitivity controlled dual input fire detector
US4345612A (en) * 1979-06-12 1982-08-24 Citizen Watch Company Limited Anesthetic gas control apparatus
US4335379A (en) * 1979-09-13 1982-06-15 Martin John R Method and system for providing an audible alarm responsive to sensed conditions
CN110164066A (zh) * 2017-12-29 2019-08-23 郑州天舜电子技术有限公司 一种安全警戒指示灯

Also Published As

Publication number Publication date
NL7313897A (nl) 1975-04-14
JPS5067197A (enrdf_load_stackoverflow) 1975-06-05
FR2247773B1 (enrdf_load_stackoverflow) 1977-09-16
DE2402493A1 (de) 1975-04-30
FR2247773A1 (enrdf_load_stackoverflow) 1975-05-09
BE808064A (nl) 1974-03-15

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